hmm i am trying this i would assume that you just go into any random folder click on the tools tab, then click folder options, then click the file types tab in this, find the icon you want to change, then click the advanced button,then click change icon, and browse then change it to the one you want.(note before you do this you might want to shift icons to a folder in the program files or sumthing because when you try to move it after applying the icon it will probably screw them up)
hope this helps
hmm scrap that i just tried it and it changed all of my file settings so when i double click on them it tries a search instead of opening them lol